Each day, millions of people travel by air planes, trains, buses and cars (collectively referred to herein as passenger carriers). Many passengers spend multiple hours inside air planes during a single trip. Oftentimes, they desire to have a good sleep while sitting in their seats. The passengers have the option of tilting their seat backs backward for better rest. However, due to limited space on air planes and other types of passenger carriers, the seat backs at the reclined position are still substantially upright. With their backs in an upright or close to upright orientation, people cannot sleep well. For instance, their heads often make a sudden forward nodding motion that can wake them up when they attempt to sleep in passenger carriers. As another example, in such a situation, their heads tend to tilt left or right. The side tilting causes neck pain. It also causes passengers to tilt their body left or right and thus interfere with neighboring passengers.
Accordingly, there is a need for a new head restraint device that restrains the range of motion of a passenger's head while the passenger is sleeping. The new head restraint device needs to absorb shock that is created when the passenger's head nods forward or tilts to side while still provides sleep comfort for the passenger. Furthermore, the new head restraint device needs to fit seat backs of different sizes. Moreover, the new head restraint device needs to fit seat headrests of different sizes as well. In addition, the new head restraint device needs to function with different types of seat headrests.